Along with huge progress of living standard and health care service, life expectancy of human is prolonged gradually and proportion of aging population increases continuously. As for the ageing society, problems concerning social welfare, medical and pharmaceutical technologies and social security system appear and increasing aged people cannot be taken care of appropriately and adequately by their family members and their families. Therefore, sports, leisure, entertainment, etc. are among the necessary physiological monitoring items.
In order to sense the physiological signals of human body in a way that is free from foreign body sensation, a wearable sensor is the most important part. There has been technical discussion on this abroad. For example, Mr. Sergio used two conductive electrodes to sense pressure, based on a mechanism of providing a fixed frequency from an external system and sensing the capacitance between the two electrodes. The pressure changes are represented by voltage (see reference document 1). Another system used to sense breath is represented by distance changes: when a user breathes, the capacitance will change due to changes in the distances between the two electrodes (see reference document 2). Furthermore, the capacitance between the two conductive electrodes has been used to sense humidity (see reference document 3). Jun Rekimoto developed a technology capable of measuring the distance between conductive objects. He measured the capacitance between the electrodes and the conductive objects and used a transmitter and an electrode receiver. When human body approaches the two electrodes, the capacitance increases for sensing the proximity and position (proximity and position sensor). As the sensing gesture is not directly contacted with skin, equivalent parasitic capacitance is not taken into consideration. No different results are caused by different pressures, pull, or strain. In the text, watch form is adopted and a capacitance corresponds to a fox n of hand. When people sit on cloth, a shield layer is grounded, and the output end is represented by amplitude of voltage and its emitting signal is fixed and not oscillating. That is to say, it is invariable. (See reference document 4). Cliff Randell studied the situation that two pieces of conductive cloth form a capacitance, and when the posture of human body changes under the effect of external pressure, the capacitance changes along with the human body in his paper (see reference document 5). In Jan Meyer's study, his theory is as same as above ones, but material between the two pieces of conductive cloth is changed (see reference document 6). Finally, in Jingyuan Cheng's study, human body is served as a medium and conductive cloth is placed at both sides of the body to form a capacitance and a circuit is employed to measure the change of capacitance. In his study, he expresses to us that breathing and drinking water can generate different distinguishable signals (see reference documents 7).
In U.S. patent Ser. No. 11/68,132P, two pieces of cloth are used to measure the physiological change of human body, but the measured parameter is voltage change by means of change in capacitance between the conductive cloth due to change of human body.
In U.S. Pat. No. 6,826,968, a medium is placed between electrodes in row and line to form capacitance to measure the pressure, which measures the change of voltage by means of the change of capacitance between the two pieces of cloth along with pressure with a fixed frequency.
In U.S. Pat. No. 6,469,524, a signal is emitted to the first electrode, and the second electrode and the first electrode form a capacitance. When people approaches, the capacitance changes and meanwhile a phase shifted signal is generated.
In patent PCT/CN2008/001571, the conductive areas at both sides of the crack change along with external force which is irrespective of contact with human body.
In US patent 2005/0215915, two electrodes are pressed to cause distance change and change in capacitance. While in the invention, change in capacitance is generated along with pressure change between the body and the electrodes or dielectric constant change between the body and the electrodes.
In patent CN2641621, two conductive materials, such as metal sheets or fiber, generate change in capacitance under effect of pressure, which is irrespective of the body of testee. And insulating materials are required between the two electrodes.
In patent CN101622518A, change in capacitance is generated by pressure and shear force on the capacitive sensor while the capacitance between non-conductive material and human body is changed due to external force.
In patent CN1718160, the static capacitance used for measuring breath further utilizes change in capacitance of two conductive materials under pressure.
In patent JP2003339652A, heartbeat and breath sensor are obtained by the change in capacitance of the two electrodes under effect of pressure.
U.S. Pat. No. 6,724,324 is capacitive proximity sensor, which includes a first electrode that receives an AC signal, a second electrode that generates an input signal. The sensor further includes an intermediate electrode placed between the first and second electrodes and a grounded end for sensing whether the finger approaches the position or not.
U.S. Pat. No. 7,676,296 provides symmetrically arranged electrodes relative to the head of the main body, which include at least a first electrode and a second electrode. The first and second electrodes are selectively coupled at an AC voltage source for sensing the posture of the head of passengers in the vehicle. The electrodes are not contacted with the testee.
In US Patent 2007/00849341, an oscillator generates a signal to measure the resistance and capacitance of characters on cloth and paper. In the invention, an oscillator, in particular an unstable state oscillator is used to measure the change in capacitance between the electrodes of the cloth and the human body. The change in capacitance is represented by resonance frequency. For example, different physiological statuses induce interaction between the electrodes of the cloth and the human body so as to generate different resonance frequencies, voltages or currents which will change continuously along with the change on human body. Different physiological statuses generate different frequency, voltage or current change curves.
U.S. Pat. No. 7,173,437 uses a capacitive sensor to measure the biopotential. However, the invention measures the resonance frequency caused by interaction between the electrodes of the cloth and the human body. The invention measures the “change” generated by “Activity” of human body.
In U.S. Pat. No. 7,135,983, an oscillating circuit is used. When people approaches the electrodes, on and off capacitances are different. Therefore, the frequencies measured by the oscillating circuit are different. But this patent is used to measure on or off capacitance and there is only one electrode. However, the invention relates to the change in capacitance between the electrodes and the human body, which is the physiological change of human body but not only on or off capacitances. The invention reads the physiological signals under long time interaction of the electrodes of cloth and the human body. In U.S. Pat. No. 7,135,983, a single electrode is used and grounded virtually so that the change in capacitance is small. Due to the parasitic capacitance of human body, the accuracy and reliability are unstable. But in the invention, a loop is formed between the two electrodes and the human body. The physiological changes of human body such as hand movement, breathing, swallowing, coughing and etc change remarkably. And for different physiological changes, the frequency, voltage or current changes are different in characteristics. Therefore, the physiological changes of the human body can be judged by means of characteristics of the frequency, voltage or current changes. That is to say, the invention measures the continuous change between the human body and the electrodes and analyzes the change of characteristics of frequency, voltage or current in continuous change but not only on or off capacitances.
Thus it can be seen that in above cited prior art, change on amplitude of voltage or frequency signal is not remarkable. Therefore, the invention improves the prior art and designs an oscillator to generate frequency and is provided with at least one piece of conductive cloth which is contacted with the human body to form capacitance. When the human body has physiological changes, the capacitance changes therewith. Therefore, the invention can sense the change of resonance frequency. The signal is remarkable and easy to judge.
The physiological signals measured by the invention are obtained by using wearable conductive cloth, in particular to sense breathing, swallowing, coughing, posture, humidity and pressure degree of each part of the human body to generate distinguishable signals. Specifically, when the capacitive sensors are in different positions, the capacitances of the capacitive sensors are different so that the voltage, current or frequency ranges measured are different so as to obtain the physiological signals at different positions.
Reference document 1. M. Sergio, et al, A Textile-Based Capacitive Pressure Sensor, Sensor Letters, Volume 2, Number 2, Jun. 2004, pp. 153-160(8).
Reference document 2. Tae-Ho Kang, et al, Sensors on Textile Substrate for Home-Based Healthcare Monitoring, Proceedings of the 1st Distributed. Diagnosis and Home Healthcare (D2H2) Conference.
Reference document 3. F. Di Francesco, D. Costanzo, P. Salvo, D. De Rossi Towards the measurement of sweat rate via wearable sensors, 4th pHealth conference 2007.
Reference document 4. J. Rekimoto, ET AL, Gesture and Gesture Pad: Unobstrusive Wearable International Devices, Proceedings of the 5th IEEE International Symposium on Wearable Computers 2001.
Reference document 5. Cliff Randell, et al, The Sensor Sleeve: Sensing Affective Gestures. Ninth International Symposium on Wearable Computers—Workshop on On-Body Sensing. October 2005.
Reference document 6. J. Meyer, et al, Textile Pressure for Muscle Activity and Motion Detection, the 10th IEEE International Symposium on Wearable Computers, 2006.
Reference document 7. Jingyuan Cheng, et al, Towards Wearable Capacitive Sensing of Physiological Parameters. 2nd Int. Conf. Pervasive Computing Tech. for Healthcare, 2008.